1. Field of the Invention
The present invention relates to a resin composition for a wiring circuit board, a substrate for a wiring circuit board, and a wiring circuit board. More specifically, the invention relates to a resin composition for a wiring circuit board, for use in the formation of insulating layers, such as a base insulating layer and a cover insulating layer, in the wiring circuit board; a substrate for a wiring circuit board in which a base insulating layer has been formed from the resin composition for a wiring circuit board; and a wiring circuit board having a cover insulating layer, etc. formed from the resin composition for a wiring circuit board.
2. Description of the Related Art
Polyimide resin has been widely used in insulating layers of a wiring circuit board, such as a base insulating layer and a cover insulating layer. Such a wiring circuit board is produced, for example, in the following manner: A solution of a polyimide resin precursor, such as polyamic acid resin, is coated onto a conductor layer comprising a copper foil or the like, dried and then cured to form a base insulating layer. These steps result in the preparation of a two-layer substrate for a wiring circuit board, which has the base insulating layer directly formed on the conductor layer. Then, the conductor layer is formed into a predetermined circuit pattern by a known patterning process such as the subtractive method. Then, a cover insulating layer comprising polyimide resin is coated onto the conductor layer of the predetermined circuit pattern to prepare a wiring circuit board.
To prevent the occurrence of warpage or curling in such a wiring circuit board, it is preferred to make the linear thermal expansion coefficient of the polyimide resin nearly as low as the linear thermal expansion coefficient of the conductor layer.
When the linear thermal expansion coefficient of the polyimide resin is decreased, however, adhesion of the polyimide resin to the conductor layer lowers. As a result, peeling between the insulating layer and the conductor layer is liable to occur, making it impossible to enhance the durability and reliability of the wiring circuit board.
The present invention has been accomplished in view of the foregoing circumstances. The object of the present invention is to provide a resin composition for a wiring circuit board; a substrate for a wiring circuit board, which has a base insulating layer containing the resin composition for a wiring circuit board; and a wiring circuit board having insulating layers, such as a cover insulating layer, containing the resin composition for a wiring circuit board, the resin composition, the substrate, and the wiring circuit board being capable of preventing warpage and curling, increasing the adhesion between the insulating layer and the conductor layer, and enhancing the durability and reliability of the wiring circuit board.
To achieve the above object, the present invention provides a resin composition for a wiring circuit board, comprising: a polyimide resin precursor; and a polyhydric phenol compound. Here the resin composition for a wiring circuit board may be used to form at least one of the insulating layers of the wiring circuit board.
The insulating layer may have a linear thermal expansion coefficient of 30 ppm or lower.
The polyimide resin precursor may be a polyamic acid resin.
The polyamic acid resin may have a repeating unit structure of the general formula (1) 
where R1 represents a tetravalent organic group, and R2 represents a divalent organic group.
The polyamic acid resin may have a weight average molecular weight of 5,000 to 200,000.
The polyamic acid resin may have a weight average molecular weight of 10,000 to 100,000.
The tetravalent organic group in the formula (1) may be selected from the group consisting of aromatic, araliphatic, aliphatic, and alicyclic tetravalent organic groups having skeletons including benzene, naphthalene, perylene, diphenyl, diphenyl ether, diphenyl sulfone, diphenylpropane, diphenylhexafluoropropane, benzophenone, butane, and cyclobutane.
The divalent organic group in the formula (1) may be selected from the group consisting of aromatic, araliphatic, aliphatic, and alicyclic divalent organic groups having skeletons including diphenyl ether, benzophenone, diphenylmethane, diphenylpropane, diphenylhexafluoropropane, diphenyl sulfoxide, diphenyl sulfone, diphenyl, benzene, and diphenoxybenzene.
The polyhydric phenol compound may be a phenolic novolak resin.
The polyhydric phenol compound may have a weight average molecular weight of 100 to 3,000.
The polyhydric phenol compound may be blended in an amount of 1 to 30 parts by weight for 100 parts by weight of the polyimide resin precursor.
The present invention also provides a substrate for a wiring circuit board, comprising an insulating layer on a conductor layer, the insulating layer being formed from the resin composition for a wiring circuit board. Here the substrate for a wiring circuit board may be a laminate composed of two layers.
The present invention also provides a wiring circuit board, further including an insulating layer on a conductor layer of a predetermined pattern formed from the substrate for a wiring circuit board, the insulating layer being formed from the resin composition for a wiring circuit board.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the detailed description to follow taken in conjunction with the accompanying drawings.